Aging, disease and injury can cause permanent tissue damage, particularly in the case of organs which have limited healing capabilities, such as the central nervous system (CNS) and cartilage. Electrical stimulation can enhance cell regeneration by altering the cellular response to stimulate repair. This has been shown on conductive materials, powered by batteries. However, once the batteries have exceeded their lifetime, they require surgical replacement, exposing patients to health risks. The challenge for the long-term use of such devices is a reliable source that generates electricity from human-activity-induced thermal and vibrational energy.
Ferroelectric materials possess an inherent polarisation, thus surface charge that varies upon a change in pressure and temperature, through piezoelectricity and pyroelectricity, respectively. Therefore, they can interact with cells through electrical signals to stimulate repair. However, common ferroelectric materials such as lead zirconate titanate (PZT) and polyvinylidene-difluoride (PVDF) contain toxic or non-biodegradable components and are thus not favourable for implantation. In this work we show successful fabrication and characterisation of biocompatible ferroelectric polymer composites in the form of thin membranes and 3D porous scaffolds.
Thin ferroelectric membranes of Polydimethylsiloxane (PDMS)-potassium sodium lithium niobate (KNLN) have been prepared via in-situ poling-dielectrophoresis to obtain high piezoelectric sensitivity while maintaining flexibility [1]. A significant improvement in piezoelectric properties of quasi 1–3 composites is achieved by a combination of dielectrophoretic alignment of the ceramic particles and poling process. The degree of structuring as well as the functional properties of the in-situ structured and poled composites are enhanced significantly compared to those of the conventionally manufactured structured composites [1,2].
3D porous scaffolds of cellulose, poly (lactic acid) (PLA) and chitosan KNLN have also been produced by freeze-casting technique; using the anisotropic solidification of a suspension to achieve aligned porosity for guiding cell outgrowth. Piezoelectric particles of KNLN of varying weight fractions (10, 20, 30 and 40%) have been integrated and poled using corona technique. The resultant composites show enhanced average pore size and interconnectivity as well as piezoelectricity ideal for soft tissue regeneration applications. This research is the first to report the fabrication and material characterisation of highly porous Cellulose-KNLN and PLA-chitosan-KNLN composites prepared by freeze casting. Morphological characterisation of the obtained microstructures has been performed and linked to the processing parameters and final properties. A poling study has also been performed to achieve piezoelectric properties. The highly interconnected aligned structures with ideal mean pore size have been obtained with PLA and chitosan freeze-cast scaffolds and enhanced with the incorporation of KNLN, up to 20wt% desirable for soft tissue applications.
References: [1] H Khanbareh, S van der Zwaag and P Groen, Journal of Intelligent Material Systems and Structures, 28(18), 2467–2472, 2017. [2] DB Deutz, NT Mascarenhas, JBJ Schelen, DM de Leeuw, Advanced Functional Materials 27 (24), 1700728, 2017.